Horizontal coke oven having plural types of brick linings for heating walls



Feb. 17, 1970 M. PERCH 3,496,067

HORIZONTAL COKE OVEN HAVING PLURAL TYPES OF BRICK LININGS FOR HEATINGWALLS Filed Jan. 27, 1967 3 Sheets-Sheet 1 mesa/ks INVENTOR. MICHAEL"PERCH BY ge M. PERCH HORIZONTAL COKE OVEN HAVING PLURAL TYPES Feb. 17,1970 OF BRICK LININGS FOR HEATING WALLS 3 Sheets-Sheet 2 Filed Jan. 27,1967 PRIOR ART F/fi 4 .INVENTOR.

MICHAEL PERcH Feb. 17, 1970 M. PERCH 3,496,067

HORIZONTAL COKE OVEN HAVING PLURAL TYPES v OF BRICK LININGS FOR HEATINGWALLS Filed Jan. 27, 1967 3 Sheets-Sheet 5 PUSHER SIDE I INVENTOR.MICHAEL PEPCH PUSHER SIDE COKE SID FIG. I!-

United States Patent 3,496,067 HORIZONTAL COKE OVEN HAVING PLURAL TYPESOF BRICK LININGS FOR HEATING WALLS Michael Perch, Pittsburgh, Pa.,assignor to Koppers Company, Inc., a corporation of Delaware Filed Jan.27, 1967, Ser. No. 612,183 Int. Cl. Cltlb /02 US. Cl. 202-139 9 ClaimsABSTRACT OF THE DISCLOSURE A coke oven having heating liner wallsconstructed of both high density and low density bricks arranged invarious patterns whereby the heat transfer profile is nonplanar, and thecarbonization pressure on the heating liner walls is significantlyreduced. The end portion of the liner walls on the coke side and the topportion of each liner wall throughout its length may be entirely of highdensity bricks.

BACKGROUND OF THE INVENTION This invention relates to coke ovens and,more particularly, to an improved heating wall liner of horizontal cokeoven batteries in which heating walls are arranged side by side in arow, in alteration, with intervening coking chambers. Each heating wallincludes a pair of spaced apart heating wall liners extending crosswiseof the battery with the walls connecting together the heating wallliners to form thereby a plurality of heating flues in each heatingwall. As is customary, a regenerator chamber is provided below eachheating wall running parallel to it, and being separated from theheating wall and coking chambers by a horizontally extending partitionor floor.

The continual search for ways to increase the throughput of a horizontalcoke oven battery has produced many improvements. Among suchimprovements is a high density silica brick (about 120 pounds per cubicfoot) that may be used in place of conventional low density bricks(about 100 pounds per cubic foot). However, certain obviousdisadvantages are apparent to the use of an all high density brick linerwall. In the first place, the cost of such a high density brick linerwall would be significantly greater than a liner wall constructed ofconventional low density brick. In the second place, the maximum wallpressure generated by coal coking in a battery lined with high densitybricks, would be significantly greater than the pressure developed bycoal coking in a battery lined with ordinary (low density) brick.Moreover, the increase in coking pressure would necessitate thickerliner walls and these would increase the cost of a coke oven batterymaterially.

The recent trend to make oven chambers higher (by as much as 50%) alsoincreases the cost thereof, not only because more bricks are used, butalso because the increased wall pressure (where all high density bricksare used) and because thicker, higher walls would be required forstructural reasons.

Heretofore, coke ovens have been constructed with all high densitysilica brick liner walls, and the through-put capacity of such coke ovenbatteries has been significantly increased, but at considerableadditional cost. On the other hand, the present invention provides asolution to the problem of providing a significantly greater through-putcapacity, but at only a slight additional cost.

SUMMARY OF THE INVENTION The invention comprises heating wall liners forcoke oven chambers comprised of bricks having at least two diiferentdensities arranged in patterns whereby the carbonization pressure on theheating wall liners due to carbonization of the coal is significantlyreduced.

For a further understanding of the invention and for advantages andfeatures thereof, reference may be made to the following description inconjunction with the drawings which show for the purpose ofexemplification several embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic perspective view of a portion of a heating linerwall in accordance with one aspect of the invention;

FIG. 2 is a schematic perspective view of a portion of a heating linerwall in accordance with another aspect of the invention;

FIG. 3 is a schematic arrangement of various patterns of bricks in linerwalls constructed in accordance with the present invention;

FIG. 4 is a schematic cross-sectional view of a coking chamber inaccordance with the prior art;

FIG. 5 is a schematic cross-sectional view of a coking chamber inaccordance with one aspect of the present invention;

FIG. 6 is a graph that schematically compares the carbonization pressurebuild-up in prior art ovens with that in ovens of the present invention;

FIG. 7 schematically shows the heat distribution during carbonization ina chamber constructed in accordance with the invention;

FIG. 8 is a schematic perspective view of a portion of the end of aheating liner wall adjacent the end fiues;

FIG. 9 is a schematic representation of a coke oven battery along alongitudinal plane, having heating liner walls constructed in accordancewith the invention;

FIG. 10 is a schematic plan view of a coke chamber and heating walls inaccordance with one aspect of the invention; and

FIG. 11 is a schematic elevational view of a heating wall liner inaccordance with another embodiment of the invention.

DETAILED DESCRIPTION Referring to the drawings, FIG. 1 illustratesschematically a portion of a heating wall 11 of a horizontal coke ovenbattery, comprised of a heating wall liner 13 and the usual tie walls15, 17 forming therebetween heating flues 19.

The heating wall liner 13 is made up of horizontal courses of refractorybrick of different density. In the lowermost course 21 shown in FIG. 1,alternate stretcher bricks are of high and low density; the higherdensity bricks 210 are shown as stippled and the lower density bricks21b are shown without stippling. Such bricks are of the type disclosedin Patent 1,782,638 to Totzek. For purposes of reference herein, a highdensity brick weighs approximately 120 pounds per cubic foot, and a loWdensity brick weighs about -110 pounds per cubic foot. It is to beunderstood that these densities are merely representative and do notlimit the invention in any way whatsoever.

It will be noted from FIG. 1 that all of the bricks in horizontal course23, next above the course 21, are of uniformly low density. Immediatelyabove the low density brick course 23 is another course of brickscomprised of alternate high 25a and low 25b density bricks, which arearranged in a manner similar to the bricks 21a and 21b in the firstcourse 21. Similarly, above the course of bricks 25 is another course 27wherein all of the bricks are of uniformly low density, and immediatelyabove this course 27 is another course wherein the bricks arealternately of high 29a and low 29b density.

FIG. 2 illustrates schematically a portion of another heating wall liner31 formed of bricks of the Totzek type laid up in horizontal courseswherein the lowermost course 33 is comprised entirely of high densitybricks; a course 35 next above is comprised entirely of bricks ofuniform low density; and the course of bricks 37, 39, 41 successivelylaid horizontally above course 35 are comprised of alternate high andlow density, as shown by the different surface markings used herein forpurposes of identification only.

FIG. 3 shows front elevational views of several liner walls whereinvarious arrangements A-E of high and low density bricks obtain. Thearrangement A corresponds to the liner wall described herein and shownin FIG. 2; and the arrangement B corresponds to the liner wall describedherein and shown in FIG. 1. Those skilled in the art will, of course,understand that liner walls similar to those of FIGS. 1 and 2 may beconstructed following the other arrangement of bricks C, D, and E ofFIG. 3. Further, the present invention is not limited to only thearrangements shown in FIG. 3, inasmuch as those skilled in the art willbe able readily to make other arrangements of bricks for particularinstallations.

FIG. 4 schematically illustrates a vertical cross-section through atypical coking chamber 43 of the prior art wherein all of the bricks 45,47 of the liner walls 46 are of uniform low density. Since such bricks45, 47 are of uniform low density, the heat transfer through these liner'walls to the coke is also uniform, and plastic seams 49, 51, thattravel normally from the heating liner surface toward a center verticalplane, are, in the prior art, substantially vertical planar plastic seamzones. In FIG. 4, the material between the plastic seams 49, 51 isunderstood to be coal that has not been heated sufficiently to becomeplastic. The material between the plastic seams 49, 51 and therespective heating wall liners 45, 47 is understood to be coke. When theplastic seams 49, 51 meet, at or near the center vertical plane of thecoking chamber 43, pressure waves are set up that act substantiallyuniformly over the entire vertical plane of contact, and these pressurewaves, acting through the formed coke, exert a substantial pressure onthe respective heating wall liners 45, 47.

Heating wall liners constructed in accordance with the invention,however, transmit heat non-uniformly and so non-uniform plastic seamsand pressure waves are thereby produced. FIG. is a vertical schematicview of a coking chamber 53 between heating wall liners 55, 57 inaccordance with one aspect of the invention. The bricks comprising theheating Wall liners 55, 57 are arranged generally in the pattern A ofFIG. 3; that is, alternate horizontal courses of bricks are comprisedentirely of high 59 and of low 61 density. For purposes of illustrationin FIG. 5, the high density bricks 59 (having a density of about 120pounds per cubic foot) are shown as stippled, whereas the low densitybricks (having a density of 100-1 pounds per cubic foot) do not have anystippling.

Since the high density bricks 59 have a higher heat transmission ratethan the low density bricks 61, the hea p etrat on nto the coa and theCQking rate opposite the high density bricks 59, is significantlygreater than the heat penetration and coking rate opposite the lowdensity bricks 61. Consequently, in the coking chamber 53, the plasticcoal seams 63, 65 have a wavy, wafilelike, sinusoidal appearance. InFIG. 2, such a wavy, wafile-like, or sinusoidal plastic seam 65 is shownperspectively in relation to the heating wall liner 31.

Referring again to FIG. 5, it is apparent that when the plastic seams63, 65 meet, they will meet at respective nodal points 67. Practically,the meeting of the plastic seams 63, 65 at the nodal points 67establishes horizontal lines of contact lengthwise of the coking chamber53, and, as the plastic seams 63, 65 continue to progress toward thecenter of the coking chamber 53, only horizontal lines of contact exist,or, at most, parallel, horizontal, narrow bands of contact areestablished. The area of contact provided by such narrow horizontalbands in such a wall is to be contrasted with the maximum planar area ofcontact established in the wall (FIG. 4) of the prior art. Accordingly,in the heating wall liner of FIG. 5, only horizontal narrow bands ofpressure are transmitted through the coke to the liner walls 55, 57, andthese bands vary vertically in position as the sinusoidal plastic seams63, 65 progress toward each other.

FIG. 6 illustrates graphically and comparatively the carbonizationpressure 69 obtained when the flat planar plastic seams 49, 51 of FIG. 4meet, and the carbonization pressure 71 attained when the nodal points67 of the sinusoidal plastic seams 63, 65 meet. It will be recognizedthat there is a considerable difference in carbonizetion pressurebetween peak 69 and 71; consequently, less stress is placed on theheating wall liners 55, 57 of the invention than on the heating Wallliners 45, 47 of the prior art.

FIG. 7 illustrates schematically a portion of the heating wall liner 57(FIG. 5), the plastic seam 65, and an isothermal curve 73 associatedwith the plastic seam 65. It will be noted that the isothermal curve 73is generally similar in shape to the plastic seam 65, but that a thermalnodal point 75 of the isotherm 65 is slightly sharper than the nodalpoint 67 of the plastic seam 65. Further, it will be noted that thedirection in which heat vectors 76 are believed to travel outwardly fromthe plastic seam are not parallel. Generally, the effective area forheat transfer to the coal is greater in a heating wall liner inaccordance with the invention, because of the sinusoidal of wave-likeeffect of the plastic seam 65 and isothermal line 73, than in theheating liner of the prior art (FIG. 4).

Generally, the total heat passing through the plastic seam 65 into thecoal, yet uncoked, is proportional to the area of the plastic seam incontact with the uncoked coal. From FIG. 7, it will be observed that thearea of plastic seam 65 per unit of length in contact 'with uncoked coalin oven chamber 53 is greater than the area of the plastic seam 49 (FIG.4) per unit of length in contact with uncoked coal in the oven chamber43. This is because the sinusoidal plastic seam 65 is longer than thevertical straight plastic seam 49.

In a typical installation, it is estimated that a sinusoidal plasticseam, such as 65, transmits at least 8 percent more heat per unit oftime than a flat vertical plastic seam such as 49. This means, then,that the wall liner 31, constructed of bricks having alternate high andlow density, may be nearly as effective as a wall liner constructedentirely of high density bricks; however, such a wall liner 31 is onlyabout one-half as expensive to make as the wall liner made entirely ofhigh density brick. In most instances, the percentage increase in heattransmission alone is of such significance that it outweighs anydisadvantages because of the additional cost of the high density brickused in such a wall.

Those skilled in the art will recognize that the arrangement of bricksin the wall liner 13 of FIG. 1 produces an isothermal front 77 that hasmountain-like peaks 78 pp t each h gh densi y isk. 21a, 25 etc. a d.such peaks meet similar peaks in an isothermal front (not shown)advancing toward it from an opposite similar heating wall liner. Whenthe respective peaks of the isothermal fronts 77 meet, they meet indistinct, short zones of contact, in contrast to continuous horizontallines of contact established when the isothermal fronts 73 mentionedhereinbefore meet, and in contrast to the vertical continuous fiat planeof contact when the fronts of the oven 43 (FIG. 4) meet. Because theisothermal fronts 77 meet in separate small zones of contact, such aheating wall liner would be subjected to much less pressure even thanthe wall 31 wherein the lines of contact are horizontal continuouslines.

FIG. 3 illustrates a few of the many other arrangements of bricks thatmay be used effectively in heating liner walls to achieve particularpurposes. Those skilled in the art will appreciate that for eacharrangement of bricks shown, there is a particular plastic seamconfiguration and isothermal front. While FIG. 3 illustrates only a fewof the arrangements that may be made, those skilled in the art willundoubtedly be able to construct other suitable arrangements to suitparticular conditions.

In some applications, heating wall liners may be constructed usingbricks of more than two densities; with or without matching patterns inopposite wall liners, as the occasion requires. Further, heating wallliners constructed in accordance with the teaching of Tucker Patent3,102,846 would include low density bricks for the intermediate courses(the thicker bricks shown in the Tucker Patent) and high density bricksfor the alternate courses (the thinner bricks shown in the TuckerPatent). This, then, would effectively even out the heat transmittedthrough such a heating wall liner, and such an arrange ment might beused when carbonization pressures are not a severe problem.

In some other instances, opposite heating wall liners may be constructedby using high density bricks (or low density brick) for one entireheating wall liner, and both high and low density bricks may bearranged, in any of the other manners suggested herein, in the oppositeheat ing wall liner. Such an arrangement of bricks in the opposite wallsof the coking chamber may be used throughout the entire coke ovenbattery.

FIG. 8 illustrates a portion of an end of heating wall liner 79 whereinthe bricks forming the end fiues 81, 81a are of high density. It will benoticed that bricks 83 disposed between the end fiue 81 and the usualbuckstay 85 are of low density which is to reduce the amount of heattransmitted to the steel structure (buckstays) of the coke oven battery.Rather, in accordance with the invention, it is desirable to increasethe amount of heat transmitted from the end flues 81, 81a only to thecoal that is to be coked.

The bricks that form the remainder of the heating wall liner 79, may bearranged in any of the Ways suggested in FIG. 3, or in any other mannerpreferred by those skilled in the art. An advantage derived from usinghigh density bricks to form the end fiues 81, 81a is found in the factthat more heat is transmitted through the high density bricks to thecoal adjacent the end flue; whereas, under the usual conditions, poorcoking adjacent the end flues is generally experienced where bricks ofuniform low density are employed.

FIG. 9 illustrates a portion of the structure of a horizontal coke ovenbattery heating wall liner 87, wherein the up er half portion 89, abovethe line AA, is constructed entirely of high density brick and the lowerportion 91 is constructed of mixed density bricks or in some cases ofuniform low density bricks. A feature and advantage of making the upperhalf portion 89 of heating wall liner 87 entirely of high density bricksis that a faster coking rate is achieved in a zone of the coking chamberwhere slower coking normally occurs. Usually, less heat reaches theupper regions of the coking chamber than is available in the bottom orlower zone of the chamber. For this reason, it requires a longer time tocoke the coal in the upper portion of the coking chamber. Likewise,coking occurs at a faster rate in the lower portion of the chamberbecause more heat is available. Therefore, in accordance with theinvention, a faster coking rate is achieved by making the courses ofbrick in the upper half portion of the heating wall liners entirely ofhigh density brick.

FIG. 10 is a schematic transverse sectional view of a typical cokingchamber 93 which tapers in the normal manner from the pusher side towardthe coke side. The heating liner walls on the coke side are frequentlthinner than the walls on the pusher side so that more heat istransmitted to the greater volume of coal on the coke side and a morenearly uniform balance in the coking rate between the pusher side andthe coke side is achieved. But, thin heating wall liners have structuraldisadvantages. In accordance with the invention, however, the portion ofheating wall liners 95, 95a on the coke side of chamber 93, from asection line B-B in FIG. 10 to the exit on the coke side, are composedentirel of high densit brick. But, in some applications, the wall liners95, 95a on the coke side may be of mixed density bricks and the linerson the pusher side may be of uniform low density bricks. Wherefore, eventhough the heating Wall liners 95, 95a are of uniform thickness, moreheat is transmitted to a greater volume of coal near the coke side ofthe chamber 93 and a more uniform wall liner temperature and a balancedcoking rate throughout the coking chamber 93 is achieved. As shown inFIG. 10, the thickness of the heating wall liners 95, 95a on the cokeside is not reduced, as is customary in some ovens, which means that thestrength of the heating wall liners is not impaired as it frequently iswhen the coke side portion of the heating wall liners has a reducedthickness.

Several features and advantages of the heating Wall liners, constructedin accordance with the invention, are apparent from the foregoing.

Heating wall liners are normally priced according to the weight of brickused rather than according to the number or volume or bricks used.Hence, a heating wall liner constructed entirely of high density brickwould be a much faster heating wall liner, but, would, on the otherhand, be substantially more costly than a heating wall liner constructedof conventional, low-density brick. A heating wall liner constructed inaccordance with the mixed-density feature of the invention, wouldprovide a significantly faster coking rate than an all low densityliner, but it would not be significantly more expensive than theconventional low density liner. Furthermore, the mixed density brickwall liner of the invention provides a coking rate that is significantlygreater than the coking rate with a conventional low-density wallconstruction, and that approximates closely the coking rate of highdensity brick wall liners.

A feature of the invention is that the heat penetration profile for aheating wall liner of mixed density bricks is non-uniform in the sensethat the heat penetration profile of heating wall liners comprisedentirely of low density brick is planar and uniform (FIG. 4). Theprofile of the mixed density brick liner of the invention, on the otherhand, has a waffie-like, sinusoidal appearance and, in some instances,the profile may even be discontinuous. In coke ovens having such heatingwall liners, the maximum will pressure 71 (FIG. 6) due to carbonizationof the coal is significantly reduced and, in some instances, the maximumpressure peak may entirely disappear. The waffle-like, or discontinuous,heat profile effect not only reduces significantly the maximum wallpressure, but also admits of the use of coals that have a greater freeswelling index without fear of structural damage to the heating wallliner.

While in a heating wall liner of conventional low density brick the heattransfer is believed to be linearly parallel toward the center linevertical plane of the oven, in an oven having heating wall liners ofmixed density bricks in accordance with the invention, the heat transferis believed to be linearly nonparallel (as suggested by the isothermline 73 in FIG. 7). Accordingly, the eifective area for heat transfer tothe coal in an oven constructed in accordance with the invention isgreater since the length and surface area of the sinusoidal orwafiie-like front is greater than the length and surface area of thefiat front, as exemplified by a conventional heating wall liner. That isto say, the coking time in an oven constructed in accordance with theinvention, is significantly reduced with only a practicallyinsignificant increase in cost of construction of a heating Wall linerdue to the use of mixed density bricks.

Although the invention has been described herein with a certain degreeof particularity, it is understood that the present disclosure has beenmade only as an example and that various modifications and changes maybe made within the scope of the invention as defined by the appendedclaims.

What is claimed is:

1. A horizontal coking retort oven having heater walls between adjacentchambers for coking coal, including spaced apart heating wall linerswith spaced apart tie walls tying said wall liners together and definingwithin each heating wall separate vertical combustion fines wherein heatis generated that is transmitted through said wall liners to carbonizethe coal in said coking chambers, the improved construction comprising:

(a) a heating wall liner of bricks arranged in horizontal courses; with(i) all of the bricks in alternate, vertically spaced apart, firsthorizontal single courses having a high rate of heat transmission; andwith (ii) all of the bricks in alternate second horizontal singlecourses disposed intermediate said first single courses having a lowerrate of heat transmission than the bricks in said first single courses.

2. In a horizontal coke oven structure including spaced apart heatingwall liners that define coking chambers and that are subdivided by tiewalls connecting said wall liners into end and intermediary heatingfines wherein heat is generated that is transmitted through the wallliners to carbonize coal in said coking chamber, the improved heatingwall liner construction comprising:

(a) first bricks having a high rate of heat transmission arranged inalternate vertically spaced-apart single courses;

(b) second bricks having a low rate of heat transmission arranged in asingle courses located intermediate said first courses in said heatingwall liners; and with (c) the portions of the heating wall liners thatdefine the side Walls of end heating fiues of such coking chambers beingconstructed of bricks having a high rate of heat transmission arrangedin contiguous courses.

3. In a horizontal coke oven structure including spaced apart heatingwall liners that define coking chambers and that are subdivided by tiewalls connecting said wall liners into heating fiues wherein heat isgenerated that is transmitted through the wall liners to carbonize coalin said coking chamber, the improved heating wall liner constructioncomprising:

(a) an upper horizontal portion of each heating wall being comprised ofa plurality of contiguous courses of first bricks having a high rate ofheat transmission; and

(b) the remaining lower portion of each heating wall liner beingcomprised of a plurality of contiguous courses of second bricks having alow rate of heat transmission.

4. The structure of claim 2 wherein:

(a) the end fiues of said heating wall liners are coma high rate of heattransmission;

(b) the upper horizontal portion of each heating wall between said endfiues is comprised of a plurality of contiguous courses of said firstbricks; and

(c) the remaining lower portion of each heating wall between said endfiues is comprised of a plurality of courses of second bricks having alow rate of heat transmission, whereby heat is transmitted to said coalat a non-uniform rate to produce an undulating plastic seam in the coalduring coking.

S. In a horizontal coke oven structure including spaced apart heatingwall liners that define coking chambers having coke discharge endportions and that are subdivided by tie walls connecting said wallliners into heating fiues wherein heat is generated that is transmittedthrough the wall liners to carbonize coal in said coking chamber, theimprovement comprising:

(a) a zone of each heating wall liner adjacent the coke discharge endportion of each coking chamber that is comprised of a plurality ofcontiguous courses of first bricks having a high rate of heattransmission.

6. In a horizontal coke oven structure including spaced apart wallliners that define coking chambers having pusher side and coke side endportions and that are subdivided by tie walls connecting said wallliners into heating fiues wherein heat is generated that is transmittedthrough the wall liners to carbonize coal in said coking chamber, theimprovement comprising:

(a) a zone of each heating wall adjacent the coke side end portion ofeach coking chamber that is comprised of a plurality of courses of bothfirst and second bricks, said first bricks having a high rate of heattransmission and said second bricks having a low rate of heattransmission; and

(b) a zone of each heating wall adjacent the pusher side end portion ofeach coking chamber that is comprised of a plurality of said secondbricks disposed in vertically contiguous courses.

7. In a horizontal coking chamber, the improved heating wall linercomprising:

(a) a plurality of bricks arranged in horizontal courses,

with the,

(i) alternate first bricks in each course having a high rate of heattransmission, and with the (ii) intermediary second bricks in eachhorizontal course having a low rate of heat transmission.

8. In a horizontal coking chamber, the improved heating wall linercomprising:

(a) a plurality of first and second types of bricks arranged inhorizontal courses with 50 (i) the first bricks having a high rate ofheat transmission and with (ii) the second bricks having a low rate ofheat transmission,

(iii) each course of bricks including spaced apart pairs of secondbricks with one first brick interposed between said pairs of secondbricks, and with (iv) the first brick of alternate courses beingcontiguous with both second bricks of each pair of second bricks of theintermediary courses. 9. In a horizontal coking chamber, the improvedheating wall liner comprising:

(a) a plurality of first and second types of bricks arranged inhorizontal courses with (i) the first bricks having a high rate of heattransmission and with (ii) the second bricks having a low rate of heattransmission, (iii) each course of bricks including spaced apart pairsof first bricks with a second brick contiguous with each first brick andwith a single brick dispersed between adjacent second bricks, and with(iv) said pair of first bricks being contiguous with the single firstbrick of each of the contiguous courses of bricks.

References Cited UNITED STATES PATENTS 3,102,846 9/1963 Tucker 2022233,259,551 7/1966 Thompson 202-267 FOREIGN PATENTS 491,278 8/1938 GreatBritain. 5 1,122,492 1/1962 Germany.

WILBUR L. BASCOMB, JR., Primary Examiner US. Cl. X.R.

